1. Field of Invention
The invention relates to a network adapter for connecting a terminal device, such as a printer or the like, to a network, and a terminal system that includes the network adapter and the terminal device.
2. Description of Related Art
If a plurality of terminal devices, such as computers, printers and the like, are to be connected to a network formed by, for example, a local area network (LAN), a telephone line or the like, a network adapter termed a print server is often used to connect the printers to the network.
FIG. 5 illustrates such a networked system construction including a network 1, a personal computer 2 connected to the network 1, a printer 3 provided as a terminal device, a manager device 4 connected to the network 1 for managing the printer 3, a print server 5 interconnecting the printer 3 and the network 1 so as to enable bidirectional communication between the printer 3 and the personal computer 2 and bidirectional communication between the printer 3 and the manager device 4.
Known as the print server 5 is, for example, a parallel interface based on the IEEE (acronym for Institute of Electrical and Electronics Engineers in USA) 1284. Signal lines of the IEEE 1284 interface and signal contents transmitted by the signal lines are exemplified in FIG. 6.
In the diagram of FIG. 6, reference character n represents a negative logic added ahead of various signals, and nStrobe represents a signal that indicates start of data transmission from the personal computer 2 to the printer 3. Data0-Data7 represent data signals that are parallelly transmitted bidirectionally between the personal computer 2 and the printer 3 at a rate of 8 bits for each operation. Furthermore, nAck and Busy represent signals by which the printer 3 indicates the status thereof to the personal computer 2. For example, the nAck signal, when switched to a low level, indicates that the printer 3 has completed receiving data and is ready to receive next data. The Busy signal, when switched to a high level, indicates that the printer 3 is presently receiving data and unable to receive other data.
Further in FIG. 6, the PE signal indicates that no print paper is set, and the Select signal indicates that the printer 3 is selected. The nAutoFd signal indicates an automatic paper feed instruction (low level) from the personal computer 2 to the printer 3. The nInputPrime signal indicates an initialization instruction from the personal computer 2 to the printer 3. The nFault signal from the printer 3 to the personal computer 2 indicates a printer error. The nFault signal switches to a low level when the printer 3 detects absence of print paper, an off-line status or an error. The nSelectIn signal indicates a power-on instruction to the printer 3. The IEEE 1284 interface makes it possible to monitor the status of the printer 3 on the basis of levels of the various signals output from the printer 3 to the personal computer 2, such as, the Busy signal, the PE signal, the Select signal, and the nFault signal.
The signal lines for the above-mentioned signals are connected to the printer 3 and the print server 5 via connecting lines 8 as shown in FIG. 5. The connecting lines 8 have on opposite ends thereof connectors 7 each of which has predetermined pins 1-36 (see FIG. 6).
Although not shown in FIG. 5, the printer 3 has a CPU, a ROM, a RAM, a bus, an input interface (I/F), and an output interface (I/F), various sensors for detecting the status of various portions, and a printing unit.
The print server 5, as shown in FIG. 6, has an external interface (I/F) 51 for sending information to and receiving information from the personal computer 2 and the manager device 4 via the network 1, an internal interface (I/F) 52 for sending information to and receiving information from the printer 3, a CPU 53, a ROM 54 storing control programs needed to execute operations in response to various requests from the manager device 4, a RAM 55 for temporarily storing data, and a bus 56.
The manager device 4 is formed by a managing computer termed a manager. The manager device 4 is designed to receive from the print server 5 management information regarding a network appliance termed an agent, for example, the printer 3, and to monitor and manage the printer 3 (agent) according to the simple network management protocol (SNMP).
The manager device 4 (manager) has a CPU. Using the CPU, the manager device 4 generates a general-purpose terminal status management command based on the SNMP and sends the command to the print server 5 in order to manage the status of the printer 3, which is a network appliance. Upon receiving the terminal status management command, the print server 5 sends the status of the printer 3 indicated based on the levels of the various signals, for example, the Busy signal, the PE signal, the Select signal, the nFault signal, and the like, back to the manager device 4.
In the IEEE 1284 interface, the Busy signal, the PE signal, the Select signal and the nFault signal from the printer 3 are the only signals that are used to determine a status of the printer 3, so that the statuses of the printer 3 that can be monitored on the basis of the levels of these signals are limited, for example, to "ON-LINE", "OFF-LINE", "NO PRINT PAPER", "PRINTER ERROR", and the like. Therefore, with the IEEE 1284 interface, it is impossible to generate a piece of status information other than the aforementioned pieces of status information, for example, "COVER OPEN", from the aforementioned signals including the Busy signal, the PE signal and the like, in order to send it back to the manager device 4. Consequently, the IEEE 1284 interface makes it impossible to manage the detailed statuses of the printer 3 by using the general-purpose commands based on the SNMP from the manager device 4.
However, since the IEEE 1284 interface is bidirectional, the personal computer 2 is allowed to issue a transmission command in order to detect a detailed status of the printer 3, and the printer 3 is allowed to send response data in response to the command to the personal computer 2. More specifically, if the personal computer 2 issues the transmission command to detect a detailed status of the printer 3, the print server 5 forwards the command to the printer 3. In response to the transmission command, the printer 3 sends response data indicating a present detailed status thereof back to the personal computer 2. The transmission command from the personal computer 2 and the response data from the printer 3 are transmitted through the print server 5 without being subjected to any particular processing.
It may be considered that detailed statuses of the printer 3, such as "COVER OPEN" and the like, can be managed through the use of general-purpose commands from the manager device 4, by, for example, storing the response data output by the printer 3 in response to the transmission command from the personal computer 2, into a storage device provided in the print server 5, which is a network adapter, and reading out the response data from the storage device and sending it to the manager device 4 when the print server 5 receives a general-purpose terminal status management command based on the SNMP from the manager device 4.
However, the transmission command issued by the personal computer 2 can be turned off by a generally-termed off command. That is, in some cases, the personal computer 2 issues a transmission cancel command that cancels a transmission command that has been issued to detect a status of the printer 3. Once such a transmission cancel command is issued from the personal computer 2, the storage device of the print server 5 does not store any more response data indicating a detailed status of the printer 3. Therefore, the storage of the print server 5 does not necessarily have the latest status information regarding the printer 3. As a result, the present detailed status of the printer 3 cannot be reliably managed.
This problem is not unique to the IEEE 1284 interface, but may also arise in other types of parallel interfaces, or in serial interfaces, such as RS-232C, SCSI (small interface computer system interface) and the like, which do not allow a special or dedicated port to be set but must use a general-purpose data port to send and receive status information.